The invention relates to a system and a method for operating a vehicle.
WO 2009060241 A1 discloses a vehicle system including a controller which, dependent upon the measured speed of the vehicle and a path information, triggers a freewheeling mode of a gearbox. The combustion engine can be switched off in order to save fuel for all functions except the steering system and the brakes of the vehicle. By saving fuel in particular operation modes of the engine CO2 emissions of the vehicle can be reduced.
DE 10 2005 003 608A1 discloses a method for operating an engine of a commercial vehicle, wherein a transmission coupled to the engine has a freewheeling mode. The engine is switched off by setting the transmission into the freewheeling mode and interrupting fuel supply to the engine in the freewheeling mode. While the freewheeling mode is enabled, the gear setting is adapted to the current speed of the vehicle.
It is desirable to provide a method for operating an engine of a vehicle which improves a CO2 balance of the vehicle.
It is also desirable to provide a reliable system for performing such a method.
A method is proposed for operating an engine of a vehicle, particularly a commercial vehicle, wherein a transmission coupled to the engine has a freewheeling mode. The engine is switched off by setting the transmission into the freewheeling mode and interrupting fuel supply to the engine in the freewheeling mode depending on one or more operating conditions of the vehicle, and, while the engine is switched off, a gear in the transmission is proactively selected depending on one or more operating actions of the vehicle anticipated to be required on or within a predefined time limit after restart of the engine.
Advantageously, fuel and emissions can be saved while the necessary support functions provided by a running engine can be re-established as fast as needed. The vehicle can be operated safely and economically. The method can be performed with existing hardware in a vehicle which can easily be used or adapted—for instance by adapting the control software of the hardware—to perform the method. Particularly, the engine can be switched off when it is recognized that no steering action will be required for a predetermined time span which is sufficient to switch the vehicle off and on again. The engine can be switched off when it is recognized that support functions for which the engine is needed, such as servo steering or servo braking, for instance, will not be needed for a predetermined time span, e.g. for several ten seconds or more, typically at least 20 seconds or at least 30 seconds. All kinds of information available in the vehicle, e.g. provided by information systems and/or control systems and/or support systems and the like, can be used which allow to anticipate a coming requirement for steering or braking within a reasonable time span.
One particular operating condition may refer to the vehicle moving downhill and straight ahead and does not need engine based braking or steering support such a servo braking function or a servo steering function within a certain time span, while the transmission is being prepared in a way (by selecting a proper gear) that the engine can provide the necessary support for such functions on or within a few seconds after restart of the engine. During the freewheeling mode, the rotatable gear components of the transmission are rotating for ensuring that the transmission components are sufficiently lubricated.
The transmission can be an automated mechanical transmission, an automatic transmission or a CVT transmission (CVT=continuously variable transmission).
In another particular operating condition the vehicle may move downhill and a very shallow bend is present or anticipated by electronic maps or a navigation system or the like, so that the vehicle can move predominantly straight ahead and does not need engine based braking or steering support such a servo braking or servo steering within a certain time span, while the transmission is being prepared in a way (by selecting a proper gear) that the engine can provide the necessary support for such functions on or within a few seconds after restart of the engine. Instead of a normal servo steering support, brake steering can be used, i.e. the steering actuator (such as a steering wheel) generates slight turning movements of the steerable wheels which can brake the wheels one side of the vehicle more than on the other side so that the vehicle can follow a shallow bend. Such steering by (selectively) braking is possible at low wheel angles not more than 10°, favourably not more than 5°, at moderate steering forces.
In another particular operating condition the vehicle may move on level ground or downhill and the driver may be desirous to brake far ahead because of a coming speed limit or a parking area or a fuel refill station. The vehicle can decelerate slowly, while the transmission is being prepared in a way (by selecting a proper gear) that the engine can provide the necessary support for such functions on or within a few seconds after restart of the engine.
According to a favourable method step, in a first case when a steering action is anticipated on or after restarting the engine, a gear in the transmission may be selected generating higher engine revolutions than when no steering action is anticipated. Alternatively, in a second case when no steering action is anticipated on or after restarting the engine, a gear in the transmission may be selected generating lower engine revolutions than would have been chosen when a steering action would have been anticipated.
Normally, in a freewheeling mode, low revolutions are selected. For instance, a twelfth gear may be engaged which results in approximately 1200 rpm. Engaging the eleventh gear would result in “high” revolutions with approximately 1500 rpm. this results in a quicker availability of steering support than lower revolutions. In a critical situation where a very quick reaction of the steering would be required it would even be possible to engage the tenth gear which would result in approximately 2000 rpm.
A favourable method step may further comprise adapting the gear as a function of a vehicle speed. In case the vehicle speed changes while the engine is switched off, an appropriate gear of the transmission can be selected and prepared for a quick restart of the engine and a quick supply of servo support for components like steering and brake devices.
A favourable method step may further comprise restarting the engine when one or more conditions are fulfilled, the conditions comprising a steering action above a predetermined steering angle and/or a predetermined steering force is required actually or anticipated within a predetermined time span;
a braking action is required actually or anticipated within a predetermined time span by activating a brake actuator;
a system responsive to approaching objects detects an approaching object;
a lane detecting system of the vehicle requires a steering action or anticipates a steering action within a predetermined time span and/or spatial range ahead of the vehicle;
an air pressure in a pressurized air system is at or below an air pressure limit;
a battery charge in a battery system of the vehicle is at or below a battery charge limit.
It is of advantage to maintain the freewheeling mode of the transmission with fuel interruption as long as possible so that a reasonable value for such time spans is, for instance, a few seconds, particularly 1 to 10 seconds before an action such as braking action, steering action is started.
A safe operation of the vehicle is possible. Expediently, the engine will not be switched off when one or more of these conditions are present or anticipated within the predetermined time span.
A favourable method step may further comprise switching off the engine only when one or more conditions are fulfilled, the conditions comprising
no steering action above a predetermined steering angle is required actually or anticipated within a predetermined time span;
no braking action is required actually or anticipated within a predetermined time span;
air pressure in a pressurized air system is available above a air pressure limit;
a battery charge in a battery system of the vehicle is above a battery charge limit, thus ensuring the safe operation of the vehicle.
It is of advantage to maintain the freewheeling mode of the transmission with fuel interruption as long as possible so that a reasonable value for such time spans is, for instance, a few seconds, particularly 1 to 10 seconds before an action such as braking action, steering action is started.
A favourable method step may further comprise prohibiting switching off of the engine in case a lane detecting system of the vehicle requires a steering action within a predetermined time limit and/or spatial range ahead of the vehicle. For instance, information provided by an adaptive cruise control system can be used.
A favourable method step may further comprise restarting the engine in case a steering angle is anticipated of at least 5°, preferably of at least 10° on or after restart of the engine. Expediently, a driver may prefer servo steering support for larger steering angles.
According to another aspect of the invention, a control system is proposed for operating an engine of a vehicle, particularly a commercial vehicle by employing a method as described above, wherein means are provided for
switching off the engine by setting the transmission into the freewheeling mode and interrupting fuel supply to the engine in the freewheeling mode depending on one or more operating conditions of the vehicle;
selecting a gear in the transmission proactively depending on one or more operating actions of the vehicle anticipated to be required on or within a predefined time limit after restart of the engine.
Expediently, the means may include a control unit which triggers switching off and on the engine and selecting a proper gear depending on the operating conditions and operating actions, respectively.
According to a favourable embodiment, the means may be coupled to a system responsive to approaching objects. For instance a driver assistance system which warns a driver in case obstacles are approaching the vehicle or vice versa can be used, for instance radar or lidar based systems which are looking ahead of the vehicle.
According to a favourable embodiment, the means may be coupled to a lane detecting system of the vehicle. Expediently, a lane detecting system can easily provide information of the kind of road ahead of the vehicle and can particularly detect whether the vehicle is approaching a bend, a junction or the like.
According to a favourable embodiment, the means may be responsive to a steering angle a and/or a steering force SF and/or a braking force BF.
According to another aspect of the invention, a vehicle is proposed, particularly a commercial vehicle, comprising a control system as described above. The vehicle allows to drive in an economic and safe way.
According to another aspect of the invention, a computer program comprising a computer program code adapted to perform a method or for use in a method as described above when said program is run on a programmable microcomputer. The computer program can be loaded to an appropriate read- and/or write memory of a control unit which triggers switching the engine off and initiating the freewheeling mode of the transmission when certain operating conditions of the vehicle are present. The computer program can be loaded into the control unit by attaching a disk, a USB stick, a CD, a DVD or any other appropriate data carrier. Expediently, the computer program may be adapted to be downloadable to the control unit or one of its components when run on a computer which is connected to the internet. In this case the computer program can be loaded to the control unit remotely.
According to another aspect of the invention, a computer program product stored on a computer readable medium, comprising a program code for use in a method as described above in a computer. The computer readable medium may be any kind of appropriate data carrier.